Welcome to Introduction to GIS Software: QGIS, Class 7
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Introduction to GIS Software: QGIS
in QGIS, the type of your field matters
fields have to be integer, real, text, or date
integers are numbers with no digits after the decimal
integer examples: 5, 243
reals are numbers with digits after the decimal
real examples: 0.0002, 19.4
text is a piece of text
text examples: ponies, Portugal
numbers are aligned right
text is aligned left
sometimes numbers are imported as text
this will keep you from performing numeric operations
like making a graduated style, or adding two numbers
the conversion functions will let you deal with this
to_int( [field_name] )
to_int( [field_name] )
converts text to integers
for example:
to_int( "sat_takers" )
to_real( [field_name] )
to_real( [field_name] )
converts text to decimal numbers
this isn't going to work if there are commas in the numbers
I recommend doing this kind of editing in your spreadsheet program
PLUTO has a handy field called BBL
BBLs are unique identifiers for every parcel in NYC
BBL: borough, block, and lot number
2038610014
2
2: borough code (Bronx)
203861
3861: block number
2038610014
14: lot number
this spreadsheet has no coordinates, but you can join the BBLs
source
BBLs are always 10 digits
1 digit: borough code
1 digit: borough code
5 digits: block number
1 digit: borough code
5 digits: block number
4 digits: lot number
this spreadsheet has no coordinates
source
you can build BBLs if you need to
source
concat('2', "Block", "Lot")
(don't use this, it won't work)
concat concatenates (adds) strings
here we add 2 (the borough code) and the Block and Lot fields together
but it's not ten digits long
you need to add 0s to the left of the block and lot fields
concat('2', lpad("Block", 5, '0'), lpad("Lot", 4, '0'))
attribute joins combine data based on a common column
we can also join based on a common geography
this will help us summarize data for points in a polygon
the target layer is where you want the data to be added
the join layer is where you want the data to come from
you can also use spatial joins to add data to points